If you're planning on a road trip through the US, sometimes sharing the driving can be a good idea. Particularly on long journeys, adding an additional driver to your booking can help you stay alert on the road. While some car rental companies charge a fee to add an additional driver, in some cases there is no fee for "authorized drivers".
If you rent a car with most major car rental companies in the United States, the renter's spouse, employer/employee (if traveling on company business), or companions of physically impaired customers may be considered an authorized driver. Authorized drivers do not always need to be present at the time of pick-up, and may not need to sign the additional driver form.
Additional drivers will still need to meet the same age requirements, and be able to present a valid driver's license. It is important to check the terms and conditions as some car rental companies may require authorized drivers to be present at the time of pick-up.
Read more about Additional Drivers.